Light-emitting diodes (LEDs) are manufactured by forming active regions on a substrate and by depositing various conductive and semiconductive layers on the substrate. The radiative recombination of electron-hole pairs can be used for the generation of electromagnetic radiation (e.g., light) by the electric current in a p-n junction. In a forward-biased p-n junction fabricated from a direct band gap material, such as GaAs or GaN, the recombination of the electron-hole pairs injected into the depletion region causes the emission of electromagnetic radiation. The electromagnetic radiation may be in the visible range or may be in a non-visible range. Different color LEDs may be created by using materials with different band gaps. Further, an LED emitting electromagnetic radiation at a particular wavelength range may direct the radiation towards a phosphor that absorbs the radiation and emits radiation of one or more different wavelengths. So, for example, an LED emitting non-visible light may direct that light toward a phosphor that transforms the non-visible light into visible light.
Generally, LED structures have a light-emitting layer interposed between a lower layer and an upper layer, wherein the upper layer and the lower layer have opposite types of conductivity. Electrodes are formed to contact the lower and the upper layers. Current flowing from between the electrodes and the light-emitting layer takes the least electrically resistive path. In many configurations in which the upper electrode is positioned directly above the light-emitting layer, much of the light emitted by the light-emitting layer is blocked by the upper electrode, thereby significantly decreasing the light efficiency of the LED structure.
One attempt to limit the light-blocking effect of the upper electrode to increase the light efficiency of the LED structure involves forming a dielectric layer on a portion of the light-emitting layer prior to the forming of the upper layer. The upper electrode is positioned over the dielectric layer such that current flowing between the upper electrode and the lower layer of the LED structure are forced around the dielectric layer. As a result, the current flows between the upper layer and the lower layer at locations not directly under the upper electrode, thereby limiting the amount of light blocked by the upper electrode and increasing the light efficiency of the LED structure.
The dielectric layer is typically formed by depositing and patterning a layer of silicon dioxide on the light-emitting layer. The deposition and patterning steps add additional cost and complexity to the standard LED fabrication process. Furthermore the patterning steps typically comprise an etch process that may damage the surface of the light-emitting layer and reduce its crystal quality. This damage may adversely affect the quality of the LED devices and reduce the yield.
Accordingly, there is a need for an LED device having an increased light efficiency and methods for producing such a device.